Identifying putative symbiont fungi from whole community data in an amphibian host system

Host-associated microbes can interact with macro-organisms in a number of ways that affect host health. Few studies of host-associated microbiomes, however, focus on fungi. This is partly because it is difficult to discern whether a fungal organism found in or on an ectotherm host is associating with it in a durable, symbiotic interaction versus a transient one. We seek to predict these host-microbe interactions on an amphibian, the Colorado boreal toad (Anaxyrus boreas boreas). We sequenced the ITS1 region of the fungal community on the skin of wild toads (n=124) from four sites in the Colorado Rocky Mountains, across its physiologically dynamic developmental life stages. We also sampled the common habitats used by boreal toads: water from their natal wetland, aquatic pond sediment, and upland soil surrounding the wetland. We then identified fungal taxa that could be putative symbionts of toads by using an indicator species analysis on toad versus environmental samples. We identified seven fungal taxa that were significantly associated with toad skin, and which are predicted to be putative symbionts for further study. This approach leverages sequence data from host and habitat samples to predict which microbial taxa are potential symbionts versus transient microbes, thereby condensing a large set of sequence data into a smaller list of targets for further experimental investigation.